This invention relates to a nebulization control system for an ultrasonic nebulizer and, more particularly, to a new control system, which can be applied to a device for nebulizing fluids with an ultrasonic energy, for precisely controlling the quantity of nebulization when a relatively small quantity of nebulization is required.
Recently, ultrasonic nebulizers for vaporizing fluids have been applied to humidifiers for increasing humidity in rooms, inhalation apparatuses for the treatment of respiratory diseases, beauty aids, etc.
In such ultrasonic nebulizers, especially those for inhalation therapy, narcotherapy, and humidity control in hospitals, it is required to precisely control the quantity of vaporization.
The ultrasonic nebulizer disclosed in U.S. Pat. No. 3,387,607 comprises essentially a pulse oscillating circuit and an electro-acoustic transducer or ultrasonic vibrator which is energized by the output of the circuit.
In such a nebulizer, nebulization quantity control is effected by changing the so-called duty factor, in other words, changing the cycle of oscillating time period of a pulse oscillating circuit or by changing the ratio of oscillating time period to non-oscillating time period of the pulse oscillating circuit so that the ultrasonic vibrator synchronized with the oscillation generates intermittantly ultrasonic waves of constant amplitude.
Since the time delay of nebulization after the beginning of ultrasonic vibration is approximately 0.4 second, the time period of ultrasonic vibration or pulse oscillation should be more than 0.4 second.
The nebulizer of U.S. Pat. No. 3,387,607, which changes the cycle of ultrasonic vibrating time period or the ratio of ultrasonic vibrating time period to ultrasonic non-vibrating time period with the amplitude of vibration being kept constant, has the disadvantage that a large rush current is unavoidable because the rapid increase and decrease of amplitude are involved between zero-level and nebulization-level of vibration amplitude.
Another disadvantage emanating from the rapid change of oscillation or vibration is that large sized fluid particles are produced and, especially when a small volume of fluid must be nebulized, scattering of fluid droplets is unavoidable and, hence, nebulization of uniform size fluid particles is difficult.
More particularly, in an inhalation apparatus for an inhalation therapy of respiratory tract diseases wherein the nebulized fluid medicament is inhaled, it is required to precisely control the nebulization quantity over the vast range from a very little quantity to a relatively great quantity depending on the condition of the patient.
A further disadvantage is that when the fluid medicament is of high viscosity, it is not only difficult to obtain a fine mist but also impossible to precisely control the nebulization quantity.
Therefore, a primary object of the present invention is to provide a nebulization control system for an ultrasonic nebulizer, which provides a constant and accurate particle size control over the nebulized fluid even when the quantity to be nebulized is small, thereby to produce a fine mist of medicament or the like.
It is a further object of the present invention to provide a nebulization control system which requires only a small rash current and entails a relatively small power consumption for nebulization.
Essentially speaking, the nebulization control system of this invention is such that an ultrasonic vibrator is held in partially excited state and the oscillation circuit output is increased from a non-nebulization level to a nebulization level and decreased from the latter level to the former in repetation so as to control the quantity and degree of nebulization.